In applications involving electro-optical components such as LEDs, it is sometimes important to ensure accurate alignment of these components in relation to an optical element.
In particular, this is true for applications that are “etendue critical”, i.e. where maximum efficiency is needed with minimum aperture size. Examples of these applications are camera (video or photo) flash, spotlamp, and optical fiber systems for medical applications such as endoscopy. Another example is when a LED is used as a light source in a collimator, e.g. for use in an automotive headlamp.
As it is important that the electro-optical component and the optical element are precisely aligned in relation to each other, very high accuracy is required in the mounting process. Though satisfactory alignment is feasible, it comes at a price, e.g. in terms of limitations regarding mounting process order.
One attempt to improve alignment of the electro-optical component with the optical element, has been to make the latter an integral part of a module onto which the substrate is mounted. However, this does not eliminate the problem of accurate alignment. Typically, the electro-optical component is soldered onto the carrier substrate, whereas the substrate is mounted onto the module in such a way that the electro-optical component is very accurately placed with respect to the optical component. In this process, each step has its associated tolerances, which add up to the final positioning uncertainty. In many cases, this uncertainty is too large. For example, in the case with a LED used as a source in a collimator, from an optical point of view a positioning uncertainty of at most 0.05 mm is desirable. Such accuracy is not feasible for the chain of tolerances described above.